1. Field
The present disclosure relates to a fuel injection control apparatus.
2. Description of the Related Art
As a fuel injection control apparatus of this type, there has been heretofore known one disclosed in Japanese Unexamined Patent Application Publication No. 2015-4342, for example. In an internal combustion engine in which the fuel injection control apparatus is used, the effective-compression-ratio reducing operation is performed by Miller cycle operation to set the valve closing timing of the intake valve at a timing within the compression stroke. In this fuel injection control apparatus of the related art, when the effective-compression-ratio reducing operation is being performed, and the internal combustion engine is in a transient operation, the control of the valve closing timing of the intake valve described above causes fuel blown back from the inside of the cylinders to the intake ports to flow into the cylinders. This may shift an air/fuel ratio of the air fuel mixture from a desired value, and in order to prevent this situation, a fuel injection quantity of the fuel injection valve provided to each cylinder is controlled as follows.
That is, a basic injection quantity is calculated in accordance with the operating state of the internal combustion engine, and a quantity of the fuel blown back from the cylinder to the intake port (hereinafter referred to as a “blown-back fuel quantity”) is also calculated based on the fuel injection timing of the fuel injection valve, the valve closing timing of the intake valve, the pressure in the intake manifold, and other parameters. In addition, the final fuel injection quantity is calculated by subtracting the calculated blown-back fuel quantity of the last combustion cycle from the basic injection quantity and adding the blown-back fuel quantity of the current combustion cycle to the basic injection quantity, and the fuel injection quantity of the fuel injection valve is controlled so as to achieve this calculated final fuel injection quantity. The control of the fuel injection quantity in accordance with the blown-back fuel quantity is uniformly performed for each of the multiple fuel injection valves.
While the effective-compression-ratio reducing operation is performed, a part of air fuel mixture is blown back from a cylinder in a compression stroke to the intake manifold. In an internal combustion engine having multiple cylinders, since, when one of the multiple cylinders is in a compression stroke, another one of the multiple cylinders is in an intake stroke, a part of the air fuel mixture blown back from the cylinder in the compression stroke (hereinafter referred to a “blown-back air fuel mixture”) flows into the other cylinder in the intake stroke through the intake manifold, and the remains of the blown-back air fuel mixture tend to stay in the intake manifold. The air fuel mixture staying (hereinafter referred to as the “residual air fuel mixture”) flows into another cylinder in the next and subsequent strokes, which is in an intake stroke at that time. In addition, fresh air also flows into a cylinder in an intake stroke from the intake main passage connected to the intake manifold. As describe above, while the effective-compression-ratio reducing operation is performed, fresh air, the blown-back air fuel mixture, and the residual air fuel mixture flow into a cylinder in an intake stroke.
In this case, since the intake main passage introducing the fresh air is connected to the cylinders via the intake manifold, a cylinder farther from the intake main passage among the multiple cylinders receives less inflow of fresh air and more inflow of blown-back air fuel mixture and residual air fuel mixture. As a result, even if the same quantity of fuel is supplied to each of the multiple cylinders, the air/fuel ratio of the burned air fuel mixture in a cylinder farther from the intake main passage is richer than in other cylinders. Accordingly, while the effective-compression-ratio reducing operation is performed, the air/fuel ratios of the air fuel mixture in the multiple cylinders are not equal to each other and may vary.